The present invention relates to a connector for securing a first generally cylindrical member, such as a production riser, to a second generally cylindrical member, such as a subsea wellhead. More particularly, the invention relates to a connector which comprises a locking mandrel that includes a stepped surface which engages a corresponding stepped surface on a lock ring to thereby force the lock ring into locking engagement with the second member.
Tieback connectors are commonly used to secure production risers to subsea wellheads. Since the production riser extends to a surface vessel which is located a considerable distance from the wellhead, the production riser is typically subjected to sizeable forces which give rise to substantial separation forces between the tieback connector and the wellhead. Thus, the tieback connector must be able to maintain a sealed connection to the wellhead in the presence of these separation forces. In the past, this was accomplished by making the locking mandrel and the lock ring sufficiently large to withstand the separation forces. However, this in turn required the overall diameter of the tieback connector to be relatively large, which is undesirable when working from certain types of surface vessels.